Genomic analyses of human cancers have provided a detailed portrait of the mutational events that underlie tumorigenesis. This information has led to the development of targeted therapies that exploit the unique dependencies of cancer cells not shared by their normal counterparts. Although targeted approaches may offer a greater therapeutic window compared to conventional chemotherapies, their utility has been limited due to the prevalence of acquired resistance and the inability to target gene loss. While targeted therapies can elicit remarkable clinical responses, their duration is often limited as tumors acquire resistance. For the majority of drugs, the cellular mechanisms and pathways underpinning this process remains largely unknown. Furthermore, unlike oncogenic lesions, inactivating mutations that result in a loss of gene function cannot be directly targeted. Though these mutations may confer additional liabilities to cancer cells, uncovering potential genetic vulnerabilities remains a challenging task. To address both of these limitations, we have developed a novel method for conducting genetic screens in mammalian cells which relies on the bacterial Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) system to induce targeted mutation. We have performed several preliminary screens in two human cancer cell lines. Based on these experiments, we propose screening strategies to (1) uncover the genetic basis of acquired resistance and (2) identify synthetic lethal interactions with the loss o tumor suppressor genes. Specifically, we aim to: 1) Elucidate mechanisms of acquired resistance to ponatinib 2) Identify synthetic lethal interactions with loss of components of the SWI/SNF chromatin remodeling complex While we will focus our efforts on ponatinib and the SWI/SNF complex, the approaches described in our proposed work will serve as a general template that can be applied to any drug or genetic lesion. These systematic studies may also yield general insights into mechanisms of acquired resistance and synthetic lethality. Finally, results from this work may lead to improvements in existing targeted anti-cancer therapies and the development of novel targeted anti-cancer therapies.